The present invention relates to electroslag melting of metals and, particularly, to a method and apparatus for producing castings having one end portion of a larger cross-section, such as workpieces for connecting rods, piston rods, valves of ship engines by electroslag casting of metals.
Most frequently such workpieces are made from steel by forging pressing. With electroslag melting one can produce metals suitable for manufacture of vital parts. These metals have a minimum content of detrimental impurities and a high degree of chemical and physical homogeneity. The electroslag melting is known to be used, at present, for producing a great variety of ingots relatively simple in form. However, attempts to produce shaped castings encounter a number of difficulties.
For producing castings of a variable cross-section by electroslag melting use is made of either one consumable electrode of a variable cross-section or several electrodes having different cross-section, and during the whole melting operation the electrode (electrodes) is melted being connected to the electric power source applying one and the same circuit arrangement which is, as a rule, a single-phase "electrode-bottom plate" circuit. (cf. Latash Yu. V;, Medovar B. I. "Electroslag Remelting," "Metallurgia" Publishers, Moscow, 1970, pp. 125-127/in Russian/).
At present the main types of commercial installations for electroslag melting are single-phase (single-electrode) installations used for casting conversion ingots of square section and ingots of round cross-section for forging.
Certain conventional single-phase apparatus for electroslag casting of ingots are provided with uncompensated power leads having a great length of a circuit comprising an electrode made, in most cases, of magnetic steel and therefore having a high reactance and relatively low operating characteristics and hence low economic factor.
With an increase of the ingot weight and cross-section the electrode cross-section has also to be increased. As a result electroslag melting requires still heavier and heavier current. The reactance of the existing single-phase apparatus considerably increases with the increase of the ingot weight and a cos Y value and the efficiency drop below permissible limits.
In addition, in the existing single-phase apparatus due to the gradual shortening of the consumable electrode, the circuit length and shape considerably change in the process of melting, which brings about a voltage change on the slag pool and changes conditions of the electrode melting and metal solidification, which, in turn, affects the metal quality.
The problem of the efficiency of utilization of the useful electric power has been solved in an apparatus which was disclosed and claimed in the British patent specification, No. 1,117,202 granted to the present applicant. In this apparatus it has been proposed to connect two electrodes in series in a circuit with the secondary winding of the single-phase transformer, which will cause the current to flow from one electrode through the slag pool and partially molten metal to the second electrode. In this electric circuit, which will be called furtheron an "electrode-electrode" circuit, all elements thereof are arranged anti-parallelly at a distance providing for its compensation, like in a bifilar winding of resistors.
In producing castings with a variable cross-section, applying the existing installations for electroslag melting, there arise difficulties in selecting consumable electrodes which would ensure a uniform filling of the mould without reduction of the power factor.
In producing the above castings on the single-phase installations with one (or several) consumable electrodes connected in an "electrode-bottom plate" circuit, in addition to the above difficulties, there arises a necessity to readjust the installation when a part of the mould, having a larger cross-section, is to be filled with metal. For this purposes either several electrodes or one electrode of a large cross-section should be used.
On the other hand, production of castings of said shape on the single-phase installations equipped with at least two electrodes connected in an "electrode-electrode" circuit, in spite of improved economy, presents difficulties in filling with metal a part of the mould, having a smaller cross-section, when the electrodes are arranged to provide for a uniform filling of that portion of the mould, which has a larger cross-section. This is acounted for by the fact that the electrodes are impossible to be introduced into the part of the mould, having a smaller cross-section.
Disclosed in U.S. Pat. No. 3,783,168 and British patent specification No. 1,362,889 is apparatus for the production of castings by electroslag melting of metals, comprising a cooled mould mounted on a bottom plate connected through a switch to one of the two terminals of the electric power source, and at least two consumable electrodes one of which is connected to the same terminal as the bottom plate, and the second electrode being connected to the other terminal of the electric power source. This apparatus provides for the production of a great variety of ingots of a relatively simple form. However attempts to produce shaped castings, and, in particular, castings of the above shape, encounter difficulties mentioned above.